1 /* Copyright (c) 2007-2023. The SimGrid Team. All rights reserved. */
3 /* This program is free software; you can redistribute it and/or modify it
4 * under the terms of the license (GNU LGPL) which comes with this package. */
6 #ifndef SIMGRID_MC_ODPOR_EXECUTION_HPP
7 #define SIMGRID_MC_ODPOR_EXECUTION_HPP
9 #include "src/mc/api/ClockVector.hpp"
10 #include "src/mc/explo/odpor/odpor_forward.hpp"
11 #include "src/mc/mc_forward.hpp"
12 #include "src/mc/transition/Transition.hpp"
16 #include <unordered_set>
19 namespace simgrid::mc::odpor {
22 * @brief The occurrence of a transition in an execution
24 * An execution is set of *events*, where each element represents
25 * the occurrence or execution of the `i`th step of a particular
29 std::pair<std::shared_ptr<Transition>, ClockVector> contents_;
33 Event(Event&&) = default;
34 Event(const Event&) = default;
35 Event& operator=(const Event&) = default;
36 explicit Event(std::pair<std::shared_ptr<Transition>, ClockVector> pair) : contents_(std::move(pair)) {}
38 std::shared_ptr<Transition> get_transition() const { return std::get<0>(contents_); }
39 const ClockVector& get_clock_vector() const { return std::get<1>(contents_); }
43 * @brief An ordered sequence of transitions which describe
44 * the evolution of a process undergoing model checking
46 * An execution conceptually is just a string of actors
47 * ids (e.g. "1.2.3.1.2.2.1.1"), where the `i`th occurrence
48 * of actor id `j` corresponds to the `i`th action executed
49 * by the actor with id `j` (viz. the `i`th step of actor `j`).
50 * Executions can stand alone on their own or can extend
51 * the execution of other sequences
53 * Executions are conceived based on the following papers:
54 * 1. "Source Sets: A Foundation for Optimal Dynamic Partial Order Reduction"
57 * In addition to representing an actual steps taken,
58 * an execution keeps track of the "happens-before"
59 * relation among the transitions in the execution
60 * by following the procedure outlined in section 4 of the
61 * original DPOR paper with clock vectors.
62 * As new transitions are added to the execution, clock vectors are
63 * computed as appropriate and associated with the corresponding position
64 * in the execution. This allows us to determine “happens-before” in
65 * constant-time between points in the execution (called events
66 * [which is unfortunately the same name used in UDPOR for a slightly
67 * different concept]), albeit for an up-front cost of traversing the
68 * execution stack. The happens-before relation is important in many
69 * places in SDPOR and ODPOR.
71 * @note: For more nuanced happens-before relations, clock
72 * vectors may not always suffice. Clock vectors work
73 * well with transition-based dependencies like that used in
74 * SimGrid; but to have a more refined independence relation,
75 * an event-based dependency approach is needed. See the section 2
76 * in the ODPOR paper [1] concerning event-based dependencies and
77 * how the happens-before relation can be refined in a
78 * computation model much like that of SimGrid. In fact, the same issue
79 * arrises with UDPOR with context-sensitive dependencies:
80 * the two concepts are analogous if not identical
84 std::vector<Event> contents_;
85 Execution(std::vector<Event>&& contents) : contents_(std::move(contents)) {}
88 using Handle = decltype(contents_)::const_iterator;
89 using EventHandle = uint32_t;
91 Execution() = default;
92 Execution(const Execution&) = default;
93 Execution& operator=(Execution const&) = default;
94 Execution(Execution&&) = default;
96 size_t size() const { return this->contents_.size(); }
97 bool empty() const { return this->contents_.empty(); }
98 auto begin() const { return this->contents_.begin(); }
99 auto end() const { return this->contents_.end(); }
102 * @brief Computes the "core" portion the SDPOR algorithm,
103 * viz. the intersection of the backtracking set and the
104 * set of initials with respect to the *last* event added
107 * The "core" portion of the SDPOR algorithm is found on
108 * lines 6-9 of the pseudocode:
110 * 6 | let E' := pre(E, e)
111 * 7 | let v := notdep(e, E).p
112 * 8 | if I_[E'](v) ∩ backtrack(E') = empty then
113 * 9 | --> add some q in I_[E'](v) to backtrack(E')
115 * This method computes all of the lines simultaneously,
116 * returning some actor `q` if it passes line 8 and exists.
117 * The event `e` and the set `backtrack(E')` are the provided
118 * arguments to the method.
120 * @param e the event with respect to which to determine
121 * whether a backtrack point needs to be added for the
122 * prefix corresponding to the execution prior to `e`
124 * @param backtrack_set The set of actors which should
125 * not be considered for selection as an SDPOR initial.
126 * While this set need not necessarily correspond to the
127 * backtrack set `backtrack(E')`, doing so provides what
128 * is expected for SDPOR
130 * See the SDPOR algorithm pseudocode in [1] for more
131 * details for the context of the function.
133 * @invariant: This method assumes that events `e` and
134 * `e' := get_latest_event_handle()` are in a *reversible* race
135 * as is explicitly the case in SDPOR
137 * @returns an actor not contained in `disqualified` which
138 * can serve as an initial to reverse the race between `e`
141 std::optional<aid_t> get_first_sdpor_initial_from(EventHandle e, std::unordered_set<aid_t> backtrack_set) const;
144 * @brief For a given sequence of actors `v` and a sequence of transitions `w`,
145 * computes the sequence, if any, that should be inserted as a child a wakeup tree for
148 std::optional<PartialExecution> get_shortest_odpor_sq_subset_insertion(const PartialExecution& v,
149 const PartialExecution& w) const;
152 * @brief For a given reversible race
154 * @invariant: This method assumes that events `e` and
155 * `e_prime` are in a *reversible* race as is the case
158 std::optional<PartialExecution> get_odpor_extension_from(EventHandle e, EventHandle e_prime,
159 const State& state_at_e) const;
161 bool is_initial_after_execution(const PartialExecution& w, aid_t p) const;
162 bool is_independent_with_execution(const PartialExecution& w, std::shared_ptr<Transition> next_E_p) const;
165 * @brief Determines the event associated with
166 * the given handle `handle`
168 const Event& get_event_with_handle(EventHandle handle) const { return contents_[handle]; }
171 * @brief Determines the actor associated with
172 * the given event handle `handle`
174 aid_t get_actor_with_handle(EventHandle handle) const { return get_event_with_handle(handle).get_transition()->aid_; }
177 * @brief Returns a handle to the newest event of the execution,
178 * if such an event exists
180 std::optional<EventHandle> get_latest_event_handle() const
182 return contents_.empty() ? std::nullopt : std::optional<EventHandle>{static_cast<EventHandle>(size() - 1)};
186 * @brief Returns a set of events which are in
187 * "immediate conflict" (according to the definition given
188 * in the ODPOR paper) with the given event
190 * Two events `e` and `e'` in an execution `E` are said to
193 * 1. `proc(e) != proc(e')`; that is, the events correspond to
194 * the execution of different actors
195 * 2. `e -->_E e'` and there is no `e''` in `E` such that
196 * `e -->_E e''` and `e'' -->_E e'`; that is, the two events
197 * "happen-before" one another in `E` and no other event in
198 * `E` "happens-between" `e` and `e'`
200 * @param handle the event with respect to which races are
202 * @returns a set of event handles from which race with `handle`
204 std::unordered_set<EventHandle> get_racing_events_of(EventHandle handle) const;
207 * @brief Computes `pre(e, E)` as described in ODPOR [1]
209 * The execution `pre(e, E)` for an event `e` in an
210 * execution `E` is the contiguous prefix of events
211 * `E' <= E` up to by excluding the event `e` itself.
212 * The prefix intuitively represents the "history" of
213 * causes that permitted event `e` to exist (roughly
216 Execution get_prefix_before(EventHandle) const;
219 * @brief Whether the event represented by `e1`
220 * "happens-before" the event represented by
221 * `e2` in the context of this execution
223 * In the terminology of the ODPOR paper,
224 * this function computes
228 * where `E` is this execution
230 * @note: The happens-before relation computed by this
231 * execution is "coarse" in the sense that context-sensitive
232 * independence is not exploited. To include such context-sensitive
233 * dependencies requires a new method of keeping track of
234 * the happens-before procedure, which is nontrivial...
236 bool happens_before(EventHandle e1, EventHandle e2) const;
239 * @brief Extends the execution by one more step
241 * Intutively, pushing a transition `t` onto execution `E`
242 * is equivalent to making the execution become (using the
243 * notation of [1]) `E.proc(t)` where `proc(t)` is the
244 * actor which executed transition `t`.
246 void push_transition(std::shared_ptr<Transition>);
249 } // namespace simgrid::mc::odpor